Rare Earth hypothesis. Early on in this people realised that if aliens exist they would have been here long time ago. Science fiction authors like AC Clarke wrote books about aliens leaving watchers (The Sentinel ) and scientists like Fermi asked why they were not here with von Neumann machines.

I think that all other explanations have to have additional parameters such as a generalised desire not to communicate or a generalised desire to leave some societies isolated. It just violates the principle of parsimony for anything else to be the most likely explanation.